1. Field of the Invention
The problem of monitoring a possible drift of a vessel that lies at anchor, especially in darkness and in bad weather conditions, is known of old and has led to the institution known to the professionals as anchor watch. This comprises the periodic check of the ship's exact position by a member of the crew, usually by taking sights of landmarks. However, this solution is not entirely adequate for the crews of the present-day, numerous pleasure crafts, which are mostly crewed by amateurs. Moreover, the crews of such vessels often lack the experience, largely available in former days on small ships, which allows to decide on grounds of the weather conditions, whether there is a need to keep an anchor watch, which generally is considered an unpleasant duty.
2. Description of the Prior Art
Even the most modern navigation instruments like the depth sounder or Satnav are still not precise enough to register in good time the small changes in the position of a ship which indicate that an anchor is being pulled or has broken out.
SUMMARY OF THE INVENTION
It is, therefore, an aim of the invention to provide a method for monitoring possible shifts in the position of a ship lying at anchor, and also to provide a device which allows to implement the method. In consequence the invention is defined as set forth in the claims.
Extensive experiments have shown that one may fix commercially available, comparatively cheap acceleration pick-offs to a body in order to determine from their output signals whether the body which lies on the ground (and which may be fastened to an anchor or not) remains at rest or whether it is being pulled along the ground. Distinguishing such signals by means of an electronic receiver station on board a vessel, to which the body is attached by a rope or the like, provides a very appreciable safety measure, particularly in bad weather and when visibility is poor.